5 Answers
5

I use gEDA/PCB. The file formats are open and ASCII. The open file
formats make a wide variety of EDA automation tasks possible. The
ASCII format makes them easy.

I have switched from Eagle to gEDA/PCB. I have found gEDA to be a more
productive tool. The schematic capture is better but the PCB layout
seems more difficult. The scriptability is what has made the
difference. There are also tools for simulation.

Be careful of choosing a free version of an EDA tool that is crippled
or a tool that locks you in to a specific PCB vendor. There is a
learning curve associated with any EDA tool or other complex piece of
software. It will be very time consuming to switch tools.

The footprint library that I use is available at
http://www.luciani.org Also I have a variety of EDA automation scripts
on my site.

As an example of gEDA/PCB I did a remix of the Drawdio circuit design
that ladyada did (CC 3.0 BY-SA). The remix includes the EDA files and
documentation. All of the files are at
http://wiblocks.luciani.org/remix/index.html

The de facto standard (at least acc. to my impressions) is Eagle CAD. It is not open source, but there is a free non-commercial license availlaible. It is limited in PCB production (2 Layers, 10x16cm) and can handle only one schematic sheet.

I like it a lot.

A good open source alternative is Kicad. But I have not used it often enough to give good advice.

You haven't said what your schematic is for. If it's purely an illustrative schematic-- one that won't be used to generate a netlist (and/or PCB) --then you may find that general-purpose drawing tools work very well, often much better than engineering applications.

For example, we often publish circuit diagrams on our blog, and write up projects that we contribute to books and magazines as well. In situations like this, I use Inkscape to make great looking schematic diagrams that show exactly what I want to show. (You can see a few examples in this article.)

If you need to use a dedicated schematic package, as part of a PCB layout, then I'd also recommend gschem, part of the gEDA suite. It produces very clean vector-pdf output that make for good looking printouts. It has the limitations that other EDA tools have-- a learning curve and less control over the visual output than an illustration package like Inkscape.

v6 also has XML file formats that are able to be manipulated with ease, and Eagle has always had plain-text scripting and macros. I own the professional edition, but for simple boards and hobbyiest use, the free version is unencumbered and easy to use. Not sure if it makes a difference, but it's also multi-platform (OSX, Windows and Linux).
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akohlsmithOct 5 '12 at 15:35